Typical petroleum drilling operations employ a number of techniques to gather information about the wellbore and the formation through which it is drilled. Such techniques are commonly referred to in the art as measurement while drilling (MWD) and logging while drilling (LWD). MWD and LWD techniques may be used, for example, to obtain information about the well (e.g., information about the size, shape, and direction thereof) and the properties of the surrounding formation (e.g., the density, porosity, and resistivity thereof which may be related to the hydrocarbon bearing potential).
Transmission of data from a downhole tool in the drill string to the surface is a difficulty common to many MWD and LWD operations. Mud pulse telemetry techniques may be utilized for such data transmission. In mud pulse telemetry operations, data may be encoded as a series of pressure pulses that are transmitted through the column of drilling fluid to the surface. These pressure pulses are measured at the surface where they may be decoded to provide the transmitted data to the drilling operator.
Mud pulse telemetry signals are well known to be highly noisy and attenuated such that the resulting data transmission rate is generally very slow (e.g., on the order of about 1 to about 10 bits per second or even less). The noise and attenuation commonly depend on many factors including the wellbore depth, drilling fluid properties, the physical structure of the drill string, and the frequency of the transmitted signal. Signal noise and attenuation can vary widely during a drilling operation such that there is a need for improved telemetry methods that automatically select the frequency band of the mud pulse telemetry channel.